PURPOSE: To prevent a virtual computer system from cutting off undesirably interruption by incorporating other CPU, when the correspondence is different from that an operation system has, in case of the rise of the virtual computer system.

CONSTITUTION: The rise of a virtual computer system is executed from a console, and a test I/O instruction TIO is generated. As a result, a channel control device (a common CHP) used for the virtual computer system is selected and confirmed, and subsequently, a CPU and a common CPU connected to the system are confirmed. Next, when the selected CHP and the CPU are in an odd- even or even-odd relation, a switching processing of the common CPU is executed. That is to say, for the time being, #1CPU1-1 being the common CPU generates a signal processor instruction to other CPU1-0, restarts the CPU 1-0, and the own CPU1-1 stops. That is to say, an interruption mask is opened so that #0CPU1-0 receives an interruption request from the channel control device of an even number.